1. Field of the Invention
The present invention relates to an image forming apparatus having a mode in which plural colors are overlaid together to form a color image and a mode in which a monochrome image is formed, a correction control method executed in the image forming apparatus, and a computer readable information recording medium storing a correction control program for causing a computer to execute the correction control method.
2. Description of the Related Art
In an image forming apparatus of an electrophotographic type, generally speaking, an image is formed for each color, and four colors of images are overlaid together to form a visible full-color image. As image forming apparatuses that form images in such a manner, a tandem-type color image forming apparatus is known, for example. Tandem-type color image forming apparatuses include one in an indirect transfer type and one in a direct transfer type.
On an intermediate transfer belt on which an image carried by an image carrying member is primarily transferred in the former type, or on a conveyance belt that conveys transfer paper on which an image carried by an image carrying member is directly transferred in the latter type, a correction pattern for color matching is formed for each color. In the tandem-type image forming apparatus, the correction patterns are read by means of optical sensors, writing timing is corrected, and adjustment is executed such that positions at which the respective four color images are overlaid become coincident.
In the tandem-type image forming apparatus, ordinarily, so-called color mode in which a color image is formed and a monochrome mode in which a monochrome image is formed are set, an operator selects either one of these modes from an operating panel, and the selected mode is executed. It is noted that, the color matching correction is called color matching correction because respective positions at which the four color images are formed are made coincident. Further, because color matching correction means correction of an error in respective positions at which the four color images are formed, color matching correction is also called positional error correction. Therefore, the color matching correction and the positional error correction are technically equivalent.
In the above-mentioned image forming apparatus in the related art in which the four colors are overlaid together and a color image is formed, color matching correction and tone correction for a color image are executed also in forming a monochrome image. In this case, the tone correction is such that a toner image (patch) is formed on a photosensitive drum or such, the toner patch is read by a tone sensor, and correction is executed. Therefore, large amounts of toners are used other than those for an image which a user actually wishes. In addition, also in the monochrome mode in which an image is formed by using only a black toner, the color patch is formed and tone correction is executed. Therefore, even in the monochrome mode, color toners are consumed.
As a technique for reducing such a useless consumption of color toners, for example, techniques discussed in Patent Documents 1, 2 and 3 (below mentioned) are known. Among these documents, Patent Document 1 (Japanese Laid-Open Patent Application No. 2008-151855) discusses a color image forming apparatus in which a white and black control mode in which tone correction is executed only for a black toner and a color control mode in which tone correction is executed for the black toner and color toners are executable. Then, at least one of the white and black control mode and the color control mode is selectively set, and the set control mode is executed.
Further, Patent Document 2 (Japanese Laid-Open Patent Application No. 2008-197542) discusses a job receiving part that receives an image to print as a printing job, and a correction control part that forms an image to print in any one of modes in which image forming conditions are different, and also, causes an image forming part to form an adjustment pattern, causes a measuring part to measure the adjustment pattern, and executes correction of an image forming condition for each mode. Further, the Patent Document 2 discusses a cumulative operation managing part that calculates and stores cumulative operation information after previous correction, and a process control part that, prior to forming an image to output, determines a mode suitable for the image, and determines whether to execute correction, by comparing the cumulative operation information with a threshold that is determined for each mode.
Further, Patent Document 3 (Japanese Laid-Open Patent Application No. 2009-053668) discusses an image forming apparatus. The image forming apparatus includes a transfer belt, photosensitive members provided for respective colors of YMCK that are used to form a black adjustment pattern and color adjustment patterns on the transfer belt, a pattern sensor that detects the black adjustment pattern and the color adjustment patterns, a monochrome adjustment part that adjusts a black image tone, a color adjustment part that adjusts yellow, cyan and magenta image tones, and an adjustment operation determining part that determines whether only adjustment by the monochrome adjustment part is executed or only adjustment by the color adjustment part is executed, based on color of an image to be formed on recording paper. Among these parts, the monochrome adjustment part adjusts the black image tone in a case where the black adjustment pattern is formed, and the color adjustment part adjusts image tones of yellow, cyan and magenta in a case where the color adjustment patterns are formed.
In each of the techniques of the Patent Documents 1-3, in the monochrome mode, correction for monochrome is executed manually or automatically, and, in the color mode, correction for color is executed manually or automatically. Thus, useless consumption of color toners is reduced in the monochrome mode.
However, in consideration of the contents that are set, usage situations and so forth in the image forming apparatus, useless correction for monochrome or color may be executed. That is, for example, at a time of starting up the image forming apparatus, correction for a full-color image, i.e., the tone correction of the color mode and color matching correction are executed, and, after both types of correction have been finished, it is determined whether a monochrome or color image is to be formed according to a job, and image forming is executed based on a mode according to the determination result.
That is, according to the techniques of the Patent Documents 1-3, at a time when a mode is determined manually or automatically, a correction operation suitable to the mode is executed. However, at a time of starting up the image forming apparatus, determination of a mode is not executed before tone correction and color matching are executed. Therefore, even in a case where a printing job that is to be executed first after starting up the image forming apparatus is of the monochrome mode, the job can be started after the tone correction and color matching are executed for all of the four colors. Therefore, in the case where the printing job to be executed first after starting up the image forming apparatus is of the monochrome mode, a time is required before actually starting the printing job, and also, the color toners are uselessly consumed.
In a common image forming apparatus, in particular, a digital MFP (Multi-Function Peripheral) including at least two of a copy function, a facsimile function and a printer function, mostly monochrome printing is executed, and color printing is executed a little. Further, in a network printer or a network MFP which is connected to a communication network, monochrome printing is executed more than color printing.
For example, in a MFP in which monochrome printing is set, even when correction for color is executed immediately after a condition for executing correction for color is met, a likelihood that a color printing job is given subsequently is low. Further, in a MFP in the related art, in a case where a condition for executing correction for monochrome is met after correction for color is executed, useless correction for monochrome may be executed. That is, in a MFP in the related art, it may not be said that correction for monochrome or color is executed in appropriate timing.